Adult: As 0.3% eye drops: Instil 1-2 drops into affected eye(s) every 4 hours. Severe: Initially, 1-2 drops every 15-20 minutes, gradually reduce frequency as the infection is controlled. As 0.3% eye ointment: Apply a small amount (approx 1/2 inch ribbon) into affected eye(s) 2-3 times daily. Child: Same as adult dose.
Otic/Aural Otitis externa
Adult: As 0.3% ear drops: Instil 2-3 drops in the affected ear(s) 3-4 times a day and at night. Child: Same as adult dose.
Parenteral Susceptible infections
Adult: For severe infections: 3-5 mg/kg daily in divided doses 8 hourly for 7-10 days, by IM or slow IV inj over 2-3 minutes or IV infusion over no more than 20-30 minutes. Alternatively, initial dose of 5-7 mg/kg once daily via IV infusion, then adjust subsequent doses according to serum gentamicin concentration. Child: <1 month 4-7 mg/kg daily; ≥1 month 4.5-7.5 mg/kg daily; ≥1 year 3-6 mg/kg daily. Doses are given as a single or in 2 divided doses.
Parenteral Bacterial meningitis, Ventriculitis
Adult: Initially, 1 mg daily via intrathecal or intraventricular inj, together with 1 mg/kg every 8 hours via IM inj.
Topical/Cutaneous Skin infections
Adult: As 0.1% cream/ointment: Apply gently to cleansed affected area 3-4 times daily. Child: Same as adult dose.
Special Patient Group
Current evidence suggests that there is an increased risk of aminoglycoside-associated ototoxicity in patients with mitochondrial deoxyribonucleic acid (DNA) mutations in the 12S ribosomal ribonucleic acid (RNA) gene, particularly the m.1555A>G mutation, including patients with aminoglycoside serum levels within the recommended range. Some cases were also associated with a maternal history of deafness. Although mitochondrial mutations are rare and penetrance is uncertain, genetic testing prior to initiation of recurrent or long-term treatment with aminoglycoside antibiotics may be considered but the testing should not delay urgently needed aminoglycoside treatment.
Furthermore, according to several studies, patients with mitochondrial mutations carrying the 1555G allele may have a greater risk of aminoglycoside-induced hearing loss as compared to those with the 1555A allele. Other genetic and clinical factors may also influence the risk of aminoglycoside-induced hearing loss.
Incompatible with penicillins, cephalosporins, erythromycin, furosemide, heparins, sodium bicarbonate.
Contraindications
Hypersensitivity to gentamicin and other aminoglycosides. Myasthenia gravis. Perforated tympanic membrane (otic).
Special Precautions
Patient with hypocalcaemia, hypokalaemia, hypomagnesaemia; pre-existing vertigo, tinnitus, or hearing loss; family history of ototoxicity. Patient with known m.1555A>G mitochondrial mutation. Renal impairment. Children. Pregnancy and lactation.
Adverse Reactions
Significant: Hypersensitivity, nephrotoxicity, neuromuscular blockade, respiratory paralysis, neurotoxicity, ototoxicity; superinfection (prolonged use). Blood and lymphatic system disorders: Anaemia, blood dyscrasias, purpura. Eye disorders: Ocular burning and/or irritation (ophth). Gastrointestinal disorders: Vomiting, nausea, stomatitis. Infections and infestations: Antibiotic-associated colitis. Metabolism and nutrition disorders: Rarely, hypomagnesia. Nervous system disorders: Convulsion. Renal and urinary disorders: Acute renal failure. Skin and subcutaneous tissue disorders: Erythema, pruritus (topical), rash.
Ophthalmic gentamicin may cause transient blurring of vision, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor urinalysis, urine output, BUN, serum creatinine, hepatic function (prior to, during, and after treatment); peak and trough gentamicin serum concentrations (regularly for systemic treatment). Assess hearing function prior to initiation, during and after treatment.
Drug Interactions
Additive effect with other neurotoxic and/or nephrotoxic drugs including cephalosporins, methicillin, amphotericin B, ciclosporin, cisplatin, potent diuretics (e.g. ethacrynic acid, furosemide) and neuromuscular blocking agents (e.g. succinylcholine, tubocurarine). May increase hypothrombinanaemic effect of oral anticoagulants. May antagonise the effect of neostigmine and pyridostigmine. Increased risk of hypocalcaemia with bisphosphonates. Increased risk of neuromuscular blockade with botulinum toxin. Increased plasma concentration with indometacin in neonates.
Action
Description: Gentamicin interferes with bacterial protein synthesis by binding to 30S ribosomal subunits resulting in a defective bacterial cell membrane. Pharmacokinetics: Absorption: Poorly absorbed from the gastrointestinal tract. Rapidly absorbed (IM). Time to peak plasma concentration: 30-60 minutes. Distribution: Diffuses mainly into extracellular fluids; minimal penetration to CSF and ocular tissues; diffuses readily into the perilymph of the inner ear. Crosses the placenta, enters breast milk (small amounts). Plasma protein binding: <30%. Volume of distribution: 0.2-0.3 L/kg. Excretion: Via urine (70% as unchanged drug). Plasma elimination half-life: 2-3 hours.
Chemical Structure
Gentamicin Source: National Center for Biotechnology Information. PubChem Database. Gentamicin, CID=3467, https://pubchem.ncbi.nlm.nih.gov/compound/Gentamicin (accessed on Jan. 22, 2020)
J01GB03 - gentamicin ; Belongs to the class of other aminoglycosides. Used in the systemic treatment of infections. D06AX07 - gentamicin ; Belongs to the class of other topical antibiotics used in the treatment of dermatological diseases. S03AA06 - gentamicin ; Belongs to the class of antiinfectives used in ophthalmologic and otologic preparations. S02AA14 - gentamicin ; Belongs to the class of antiinfectives used in the treatment of ear infections. S01AA11 - gentamicin ; Belongs to the class of antibiotics. Used in the treatment of eye infections.
References
Estivill X, Govea N, Barceló A et al. Familial Progressive Sensorineural Deafness Is Mainly Due to the mtDNA A1555G Mutation and Is Enhanced by Treatment with Aminoglycosides. The American Journal of Human Genetics. 1998;62(1):27-35. doi: 10.1086/301676. Accessed 01/02/2021Gao Z, Chen Y, Guan MX. Mitochondrial DNA mutations associated with aminoglycoside induced ototoxicity. Journal of Otology. 2017;12(1):1-8. doi: 10.1016/j.joto.2017.02.001. Accessed 01/02/2021Göpel W, Berkowski S, Preuss M et al. Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants. BMC Pediatrics. 2014;14(1):210. doi: 10.1186/1471-2431-14-210. Accessed 01/02/2021Aminoglycosides (Gentamicin, Amikacin, Tobramycin, and Neomycin): Increased Risk of Deafness in Patients with Mitochondrial Mutations. Medicines & Healthcare products Regulatory Agency. https://www.gov.uk/government/organisations/medicines-and-healthcare-products-regulatory-agency. Accessed 01/02/2021.Anon. Gentamicin (Ophthalmic). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 06/05/2020.Anon. Gentamicin (Systemic). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 06/05/2020.Anon. Gentamicin (Topical). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 06/05/2020.Buckingham R (ed). Gentamicin Sulfate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 06/05/2020.Cidomycin 80 mg/2 mL Solution for Injection (Sanofi). MHRA. https://products.mhra.gov.uk. Accessed 01/02/2021.Clinical Annotation for rs267606617 (MT-RNR1); Amikacin, Aminoglycoside Antibacterials, Gentamicin, Kanamycin, Neomycin, Streptomycin or Tobramycin; Ototoxicity. Pharmacogenomics Knowledgebase (PharmGKB). https://www.pharmgkb.org. Accessed 01/02/2021.Gentak Ointment (Akorn, Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 08/05/2020.Gentamicin 1 mg/ml solution for Infusion (B. Braun Melsungen AG). MHRA. https://products.mhra.gov.uk. Accessed 14/05/2020.Gentamicin 40mg/mL Injection (Hospira UK Limited). MHRA. https://products.mhra.gov.uk. Accessed 14/05/2020.Gentamicin Eye/Ear Drops 0.3% w/v (FDC International Ltd). MHRA. https://products.mhra.gov.uk. Accessed 01/02/2021.Gentamicin Intrathecal 5mg/ml Solution for Injection (Zentiva Pharma UK Limited). MHRA. https://products.mhra.gov.uk. Accessed 14/05/2020.Gentamicin Sulfate Cream 0.1% (Sola Pharmaceuticals). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 06/05/2020.Gentamicin Sulfate Ointment (Teligent Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 08/05/2020.Joint Formulary Committee. Gentamicin. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 06/05/2020.
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